Mobile and Wireless Networks
and Applications:
Introduction/Overview
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What is Mobility?
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A device that moves
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Between different geographical locations
Between different networks
A person who moves
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Between different geographical locations
Between different networks
Between different communication devices
Between different applications
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Device mobility
• Plug in laptop at home/work on Ethernet
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Occasional long breaks in network access
Wired network access only (connected => well-connected)
Network address changes
Only one type of network interface
May want access to information when no network is
available: hoard information locally
• Cell phone with access to cellular network
– Continuous connectivity
– Phone # remains the same (high-level network address)
– Network performance may vary from place to place
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Device mobility, continued
• Can we achieve best of both worlds?
– Continuous connectivity of wireless access
– Performance of better networks when available
• Laptop moves between Ethernet, Wireless LAN and
xxx networks
– Wired and wireless network access
– Potentially continuous connectivity, but may be breaks in
service
– Network address changes
– Radically different network performance on different
networks
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People mobility
• Phone available at home or at work
– Multiple phone numbers to reach me
– Breaks in my reachability when I’m not in
• Cell phone
– Only one number to reach me
– Continuously reachable
– Sometimes poor quality and expensive connectivity
• Cell phone, networked PDA, etc.
– Multiple numbers/addresses for best quality connection
– Continuous reachability
– Best choice of address may depend on sender’s device
or message content
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Mobility means changes
How does it affect the following?
• Hardware
– Lighter
– More robust
– Lower power
• Wireless communication
– Can’t tune for stationary access
• Network protocols
– Name changes
– Delay changes
– Error rate changes
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Changes, continued
• Fidelity
– High fidelity may not be possible
• Data consistency
– Strong consistency no longer possible
• Location/transparency awareness
– Transparency not always desirable
• Names/addresses
– Names of endpoints may change
• Security
– Lighter-weight algorithms
– Endpoint authentication harder
– Devices more vulnerable
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Changes, continued, again
• Performance
– Network, CPU all constrained
– Delay and delay variability
• Operating systems
– New resources to track and manage: energy
• Applications
– Name changes
– Changes in connectivity
– Changes in quality of resources
• People
– Introduces new complexities, failures, devices
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Example changes
• Addresses
– Phone numbers, IP addresses
• Network performance
– Bandwidth, delay, bit error rates, cost, connectivity
• Network interfaces
– PPP, eth0, strip
• Between applications
– Different interfaces over phone & laptop
• Within applications
– Loss of bandwidth triggers change from color to B&W
• Available resources
– Files, printers, displays, power, even routing
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Summing up
Generally, mobility stresses all resources further:
• CPU
• Power
• Bandwidth
• Delay tolerance
• Radio spectrum
• Human attention
• Physical size
• Constraints on peripherals and GUIs (modality of
interaction)
• Locations for device placement
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